//===--- ConstraintGraphScope.h - Constraint Graph Scope --------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file defines the \c ConstraintGraphScope class, an RAII object that
// introduces a new scope in which changes to the constraint graph are
// capture and will be reverted when the scope disappears.
//
//===----------------------------------------------------------------------===//
#ifndef POLARPHP_SEMA_INTERNAL_CONSTRAINT_GRAPH_SCOPE_H
#define POLARPHP_SEMA_INTERNAL_CONSTRAINT_GRAPH_SCOPE_H

namespace polar {
namespace constraints {

class ConstraintGraph;

/// RAII object that introduces a new constraint graph scope to capture
/// modifications made to the constraint graph.
///
/// Scopes are arranged in a stack, where the active scope is the top of the
/// stack. All changes made to the constraint graph are recorded in the
/// active scope. When the scope is popped (via the RAII object destructor),
/// those changes are reverted.
class ConstraintGraphScope {
   ConstraintGraph &CG;

   /// The parent scope, or null if this is the topmost scope.
   ConstraintGraphScope *ParentScope;

   /// The number of recorded changes that existed at the time this scope was
   /// formed.
   ///
   /// When this scope exits, any changes beyond this will be reverted to
   /// bring the graph back to its state prior to the introduction of this
   /// variable.
   unsigned NumChanges;

   ConstraintGraphScope(const ConstraintGraphScope&) = delete;
   ConstraintGraphScope &operator=(const ConstraintGraphScope&) = delete;

public:
   explicit ConstraintGraphScope(ConstraintGraph &CG);
   ~ConstraintGraphScope();
};

} // end namespace constraints
} // end namespace polar

#endif // POLARPHP_SEMA_INTERNAL_CONSTRAINT_GRAPH_SCOPE_H
